Three electrode crystal phase modulation receiver



June 1 1940. R Y 2,204,574

THREE ELECTRODE CRYSTAL PHASE MODULATION RECEIVER Filed Jan. 22, 1938 s Sheets-Sheet 2 June 18, 1940. M. G. CROSBY THREE ELECTRODE CRYSTAL PHASE MODULATION RECEI VER Filed Jan. 22, 19:2 3 Sheets-Sheet s FREQUENCY INV EN TOR.

40W ATTORNEY.

Patented June is, 1940 UNITED STATES PATENT THREE ELECTRODE MODULATION Murray G; Crosby, Rivtrhead, N. Y., assignor to Radio Corporation of Delaware Application January 22, 1938, Serial No. 180,273 r v (Cl. 250-) This disclosure concerns phasemoduiation ref 23 Claims ceivers of the type which utiiizeoverl0 and thereby .overor linden-compensate for its eiiect. The filters so formed convert phase modulations in wave energy into corresponding amplitude. N v

The receivers of this disclosure utilize a combination of the principles described in my Patent #2,(i85,008 dated June 29, 1937, and United States applications Serial #165,056 filed September 22,

filed March ill, 1938; Serial #178,655 filed December t, 1937, now Patent #2,156,3

2, 1939; Serial #242,469 filed November 26; 1938.

The present circuits have. an advantage in siniplicity in that a push-pull transformer is not required to obtain neutralizing voltage. i

In describing my invention reference will be made to the attached drawings wherein,

Figures 1, 2, and 3 each show the essential 30 elements of converting circuits arranged in ac reception. of phase or frequency or amplitude modulated waves in the circuit its connections; 1

Figures in. to iii are filter impedance charac teristic reactance curves and vector diagrams of modulated wave components, alli illustrating the n operation of my system;'while r j Figures 5, 6a, and 6b are filter characteristic curves used to explain the operation of all of the receivers. and in particular of the receivers when using therewith a novel signal amplifier as shown .5 in Figure 1 following the differential connected detectors.

The circuit of Figure '76 dated May and detectors to permit the.

without revising I ferric-s CRYSTAL ruasu anouwun America, a corporation 'of a band-pass filter. The crystal Hill is held in a crystal holder having a single input terminal NH and two output terminals Hi2 and Hit. The input terminal is connected to the high potential side '01 thetuned transformer Hit and put terminals are connected to the and the two output termifrequencies of these tuned 10 circuits are adjusted to be.a,,little above and a little below the resonant frequency of the crystal Pitt. This slight off-tuning produces an inductive reactance in one case and a capacitive reactance in the other case. Hence the effect will be the 16 same as though a capacity were across one of the sets of crystal terminals and an inductance across the other set. This arrangement causes the formation of two crystal filters having overand under-neutralized characteristics respectively. Thus, tuned circuit mil, tilt might be tuned capacitive to present an under-neutralized characteristic such as shown at transformer mon input terminal nals, The resonant envelopes. Consequently, the push-pull connec- 0 tion of diode resistors iii and M2 will add or aid the phase modulations and oppose and substan tially cancel amplitude modulations present on theoriginal phase modulated wave. By virtue of M the fact that one of the filter characteristics has a rejection point at a frequency lower than the carrier frequency and the otherfiiter has a rejection point at a frequency higher than the carrier .frequency, when the mean frequency of the wave M energy shifts slowly a differential voltage is available across resistors ill and M2 shunters by bypass condensers ill and I it to control the grid of a reactance tube modulator which tunes a fre quency-changing heterodyne oscillator in'the circuits prior to transformer ltil. The time control circuit RC prevents this frequency control circuit from'responding to signal modulations on the wave. ,The detected phase modulation appearing across resistors ii i and 'i it is fed 59 to an audio-frequency amplifier lit for subsequent utilization. The audio frequency amplifier the amplifier shown in Figure 1 and described in detail hereinafter may be used.

' cuits may be of any type such as shown in Figure I we and 1. The circuits of Figure 1 may. be added to the circuits of Figure 2 as indicated in the drawings by connecting the elements not shown to points'2, l, and 0.

In the circuitof Figure 2 the same principles are applied except that single. reactances I06 and I01 take the place of the tuned circuits of the prior figure connected across the crystal holder terminals and diode-driver amplifier tubes IIO' having their grids II3,- H5 and cathodes connected to the crystal output electrodes are excited by the filtered energy and are used to feed the two filtered energies to the diodes I09 and H0. Tuned bandpass (transformers I28 and I30, havingtheir primaries. shuntedby damping resistances I25 and H1 couple the anodes and cathodes of the driver tubes I09 and H0 to the diode plates Ill an H6. minals of the diode output impedances Ill and H2 may be connected to the input electrodes of any audio frequency amplifier tube supplying a utilization means or directly to a utilization means. If desired, the impedances III and H2 may be connected to an amplifier as illustrated in Figure 1. *The rectangle I20 of the figure represents the simple amplifier mentioned above and also represents an amplifier as illustrated in Figure 1'. The operation'of this circuit in other respects'is-the same as that of'Figure 1.

In the circuit of Figure 3 a discriminator is shown which utilizes a shunt connected crystal in the manner of the discriminators described in my application #167,344'flled October 5, 1937, now Patent #2,156,3'15 dated May 2, 1939. Intermediate frequencyv energy is fed to tuned transformer I00 and through isolating resistors 200 and-20l to the two terminals of the crystal holder I02 and I08. IOI' of the crystal holder is connected to the low side of the tuned transformer, Reactances X1 and X: would be either an inductance and a capacity or two tuned circuits. These reactances are adjusted so that one forms a capacitive action across the crystal holder and the other an. inductive action. The output of the two filters is taken from-terminals I02" and I03 and fed to the grids H3 and II! of diode-driver tubes I09 and 0' such as are used in Figure 2. The other features of this circuit are the same as those of Figure l'and'Figure 2.

In the operation of the receiverv of Figures 1, 2, and 3 two filter characteristics are produced to be fed to the two diode detectors I09 and H0.

The energies fed from the crystal output terminals I02 and I0! to amplifier and couplingtubes I00 and 0' of Figures 2 and 3, or directly to diode rectifiers I09 and H0 of'Figure 1, are overor under-neutralized crystal energy and have characteristics as shown in Figures 4a and do. This energy appears in transformers I20 and I30 of Figures 2 and 3 and on the diode .electrodes of Figure 1. The characteristic of the energy present on the input electrodes of I00 0! Figure .1

and in, say, transformer I20 of Figures 2 and 3, is as shown in Figure 41: beingderived from a filter of the under-neutralized type such as is obtained by under-neutralizing the and I02 by means of I00 of Figure 2 or the retially the carrier frequency,

The ter-.

The common terminal of rotation carrier are indicated by arrows attached to the side band vectors.

holder electrodes IOI actance at- X1 of Figure 3 or I00 and lli of Figure' 1. This is obtained by adjusting the said elements of the respective figures so that the reures 1 and 2 andinductive for the case or the shunt connected crystals of Figure 3. The charsay in transformer I30 the electrodes of diode acteristic of the energy, of Figures 2 and 3, or on I I0 of Figure 1 is as shown in Figure 4e, this en-' filters which are over-neuergy being passed by tralized by adjusting the elements I01 and I00 of Figure 1 or I01 of Figure 2 so that the crystal holder has an inductive reactance at substanand adjusting the reactance X: of Figure 3 so that the crystal holder has a capacitive reactance. of the shunt connected crystal, the under-neutralized characteristic is given by Figure 4e and its reactance characteristic is given by Figure 41). That is, in the case of the shunt connected filter the low impedance point on the reactance curve In the case (where the line crosses the X axis) coincides with the rejection point on the output characteristic. Also, the high impedance point on the reactance curve coincides with the carrier frequency. This is opposite to the case of the series connected filter in which the under neutralized characteristic is given by Figure 40, its reactance curve is given by 4b, the zero reactance curve coincides with the carrier frequency, and the maximum imipeiance point coincides with the rejection po n The reason for this difference between the shuntand series-connected filters is the fact.

that with the series connection the crystal allows more or less energy to flow according to its impedance, while with the shunt connection, since the drop across the crystal is utilized, the output voltage is proportional to .the crystal impedance.

In the case of Figure 4b a negative reactance is present on both sides of the carrier frequency, that is, the circuit would be capacitive on both sides of the carrier except for the very short interval near thecarrier frequency. Since the reactance is capacitive in the frequency region in which the 'side'bands are disposed and is resistive at the carrier frequency, the phase of the side bands'will be shifted 90 with respect to the carrier. In Figure 4c the carrier and side bands of a phase modulated wave are shown. The carrier is marked C, the upper side band U and the lower side band L. The positive direction of rotation is taken as counter-clockwise and the directions of the side bands with respect to the Side bands of an order greater than I has been neglected due to their small amplitude and for simplicity of explanation. when the phase modulated wave of Figure 4c is passed to the crystal having the characteristicof Figure 4a Figure 4b the spect to the carrier so that the side band relation shown in Figure 4d is and the reactance characteristic of side bands are shifted with reeffected. With the relation of Figure 4d between the carrier and side-' bands, the wave is an amplitude modulated wave,

and is suitable for detection in diode I00 or for amplification inn! and detection in diode I02. There wouldalso be an attenuation of the side bands which is not shown in Figure 411. This conversion of the phase modulated wave as of 40 to an amplitude modulated wave as of 4d tastes placein IOI, I02, I00,

"Land the converted 7 energy appears on the diode cathode or; grid of the diode driver tube III. e

The energy present in ill. of Figure 1 and of the same elements and transformers III of Figures 2 and 3 is'passed brand is a characteristic of energy in a filter having an over-neutralized characteristic and having an input-output characteristic as shown in Figure 4e, and having a reactanee characteristic as sho in Figure 4 Thus, the reactance of this last filter is positive or inductive on both sides of the carrier irequency except for a short interval near the carrier frequency; Consequently, the side bands are shifted 90 in phase by this filter also but in an opposite directionnto' the shift produced by filters having the characteristics shown in Figure 4a, Hence, the phase modulated wave as shown in Figure 4a is converted tothe amplitude modulated wave as From an examination of Figure 4d and Figure 4h, it can be seen that the side bands are approaching cancellation oi the carrier in Figure 4d and are approaching aiding the carrier in Figure 4h. Thus, the envelope of the amplitude modulations produced by the their detected output must be combined in a push-pull or series combination to reproduce the converted modulations. This combination is ei-' i'ected in the diode circuits of all of the figures by grounding the cathode of one of the diodes, say HI, and making the cathode of the other diode, say I09, the high potential side of the output circuit.

Unwanted amplitude modulationson the wave received, which are not converted to phase modulations by the action of the filters as described herein and in my United States Patent #2,085,008 1 I As stated above, the phase modulations on thewave are. in the filter circuits, converted to corresponding amplitude modulations of opposed envelopes and rectified in the diodes I09 and ii. so'that a difi'erence potential appears across the resistances i H and H2 characteristic of the sig-. nal which nray be utilized in any manner. .An additional feature of this application is the provision of a novel difierential diode combining amplifier which amplifies variations in potential in the diiierential detectors characteristic of the phase modulations on the wave and also characteristic of the amplitude modulations onwave energyv passed through the conversion circuit,

thereby adapting the receiver-to the receptionof' amplitude modulated wave energy.

More specifically, this application. also concerns an amplifier for combining the outputs of difi'erentially connected diodes such as I" and H0 of Figures 1, 2, and 3 in a manner such that either the diiferential output ora parallel combination of the outputs may be utilized without disturbing additional uses and name the connections of the diode resistors. Thus, the

amplifier is applicable to phaseand frequency amplitude moduwhich will appear which will now be from thedescription thereoi' liven.

m. inQana mshown in Figure 4h. K

: tion of the diode resistors is v two filters having 1 characteristics as shown above are 180 apart and scribed here, a

g or frequency or amplitude modulated Infrquency and phase modulation receivers in which a frequency or phase discriminator feeds diode detectors," the diode detectors must be connected diflerentially so that automatic frequency I control may be taken from the combination of I the diode voltages; This differential connection is eflectcd as shown in Figures 1, 2, and 3 by grounding the cathode of one of the diode detectors, such as for example, tube ill), and making the cathode of the other diode detector, such as fqr'example, tube I09, a high potential point. This effectively reverses the voltage across one diode resistorwith respect-to that on the other so that the two diode voltages oppose and the only output that is obtained isthat due to the difierence between the two diode voltages. This differential output is desired for the automatic fre quency controlling potentials, supplied in this particular system to RC, and is also desired fo'r the frequency and phase modul tion output. However, when it is desired to receive amplitude modulation on the same receivers, a parallel connecnecessary for proper operation although the differential connectionis necessary if automatic frequency control voltage is obtained from the same diode resistors.

By the use of the audio amplifier of Figure 1 and proper adjustment of the degree of cit-neutralization of the crystal filters the present'receiv ers may be tuned to receive either phase or am? plitude modulation. I ,have found that by adjusting the crystal filters so that one has a very small amount of negative reactance across the holder and the other a very small amount of positive reactance, a single sideband eilect is obtained as shown in Figures 6a and 612. I With the crystals almost neutralized in this way the output on the side of the carrier frequencywhich does not have therejection point is higher than the output i on the side having the rejection point. Conse quently, one of the filters exalts the carrier and selects the lower sideband and the other exalts the carrier and selects the upper sideband.

, Hence, in accordance with the principles described in my United States Patent #2,114,c35. dated April 19, 1938, these two filter outputs may be detected and combined differentially to receive phase modulation and in parallel to receive amplitude modulation. However, in the circuits of Figures 1. '2, and 3, the detectors are connected difierentially in order that automatic frequency control energy may be obtained from them. Hence, the novel combining amplifier of Figure 1 is required.

With the amplifier such as is about to be de- 65 means is provided which allows the amplitude modulation output to'be obtained from the differentially connected diodes. While the same difi'erential connections are supplying the automatic frequency control voltages used in these receivers, it will be understood that this new amplifier circuit is to be used with any phase wave receiver wherein difierential output'efi'ect is utilized when phase or frequency modulation is being received and for frequency control purposes. i The circuit of-Flg1 e 1 shows the combining amplifier connected to the differentially connected diodes at points 0-4-4). Diodes I09 and III are dififerentially connected with the diode resistor I I2 of diode ill grounded at the cathode connection and with the diode resistor iii of diode I i made high potential at the cathode connection. This combines the voltages Er and E: which appear across diode resistors so that they are 7 by choosing that diode which is fed by discrim-- I inator, filter having characteristic B which has plated waves by phase on Y discriminator circuits.

- and tube V1 receives the 'which gives minimum phase modulation receiver,

subtracted from each otherand the resultantis Ei-.E2. This subtractive resultant is that which is desired for automatic frequency control and for frequency or phase modulation wave detection.

' When it is desired to receive amplitude modulation,

the desired resultant is E1+E2. In order to obtain such a resultant, the combining system consisting of switchesS and S1, tubes V and V1 and transformer T are used. Switches S and S1 point #1 switch S1 will be units point #1 also and w en switch S is on point #2 switch S1 is also on point #2. etc. Potentiometer P divides the voltage from point "b to a value substantially equal to (E1E:)/ 2. Tubes V and Vi amplify the voltages on the arms of switches S and S1, respectively,

and combine them in push-pull in transformer T.

applied to tube V and the ,voltage (El- E2) [2 to tube V1. The resultant appearing in transformer Twould then be equal to E1 minus (Er-"E20 [2 or (EH-E2) 2. This resultant is the sum diode voltages'instead of the difference and is that desired for amplitude modulation output when the diode detectors are fed amplitude modfrequency modulation The other two positions on the switches, posi-.

. tions 3 and l, are for obtaining the outputs of each diode separately. With the arm on point 8, tube-V1 is shut off and tube V amplifies E1 which appears in the output transformer. With the arms :on point 4, tube V receives the voltage E1 voltage E1-E2. When these two inputs are combined subtractively in the push-pull output transformer, the resultant is Ei(E1-E2) or E2. These single outputs are used for testing purposes on phase modulation receivers or .are used for reducing interference. These single outputs aid in balancing the two filter characteristics and also allow the choice of the filter which gives the least interference. In other words'yinterference may be reduced by choosing the discriminator output for the frequency at which the interference occurs.

the sloping filters having characteristics as shown atA and B of Figure 5 in a frequency modulation receiver. If the interference has the frequency F1, ,9. reducedinterference'output may be obtained a minimum outputat the frequency Fi- Another instance wouldbe that F of Figures 6a and' fib in which the discriminator characteristics of a ceive amplitude modulated waves, are shown. 'Since either amplitude or phase modulation may ence occurs, say at the frequency Fgthe detector are ganged together so that when switch S is on to tube V and the voltage, =(El-E2) 12 is fed to to I the two diodes.

With the switches on point 2, the voltage E1 isof the two the frequency and 'For instance, suppose the two diodes I09 and H0 are fed by which may also 're-' be received on a single filter, when an interferwhich is being fed by a filter circuit or discriminator having the characteristic shown in Figure 6b, is chosen and that fed by'the filter or discriminator having the characteristic shown in Figure 6a. switched off. The single sideband effect of the discriminator circuit therefore reduces the effect of the interference.

I claim: 1. In a system for converting phase modulation on wave energy into corresponding amplitude modulations, an impedance on whichsaid phase modulated wave energy may be impressed, a pair of diode detectors having input electrodes and having output electrodes connected in series, an under-neutralized crystal filter circuit and an over-neutralized crystal filter circuit comprising a single piezo-electric crystal having one input electrode connected to said,impedance, and a pairof output electrodes connected to the input electrodes of said detectors, and a connection between a secondpoint on said impedance and said detector input electrodes.

2. In a system for converting phase modulations on wave energy to corresponding amplitude modulations on wave energy, an impedance energized by said phase modulated wave energy. a piezo-electric crystal having a plurality of electrodes, a first filter circuit including apair of said piezo-electric electrodes coupled to said modulations on wave energy, an impedance energized by'said phase modulated wave energy, a piezo-electric crystal having a plurality of electrodes, a first filter circuit including a pair of said piezo-electrit: electrodes connected in series with said impedance to be fed by wave energy therefrom, a second filter circuit including a pair of the electrodes of said piezo-electrlc crystal connected in series'with said impedance to be fed 'by wave energy therefrom, a detector having input electrodes coupled to each of said filter cir-' cuits, and means for under-neutralizing the capacity between a pair .of said electrodes and over-neutralizing the capacity between another pair of said electrodes. 4. In asystem for converting phase modulations on wave energy to corresponding amplitude modulations and demodulating the same, an impedance energized by said phase modulated wave energy, a. detector system having input electrodes, a piezo-electric crystal having a plurality of electrodes, a filter circuit including a pair of said piezo-electric electrodes coupling the input electrodes of'said detector system to'said impedance, asecond filter including a pair of the electrodes of said piezo-electrlc crystal coupling other input electrodes of said detector system to said impedance, and means for under-neutralizing the capacity between a pair of said electrodes and over-neutralizing capacity'between another pair of said electrodes.

15. Ina system for converting phase modulations on wave energy to corresponding amplitude modulations anddemodul'ating the same, an impedance energized by said phase modulated wave I swam energy, a detector system having input electrodes, a piezoelectric crystal having a pluralityof electrodes, is filter circuit including a pair of said piezo-eleptric electrodes and a resistance coupling the input electrodes of said detector system in shunt to said impedance, a second filter including a resistanceand a pairof the electrodes of said pie'zo-electric crystal coupling other input electrode connected to a point on said reactance said transformer connecting the input electrodes of crystal having, an additional pair of electrodes, a pair of electron discharge devices each havinga control electrode,

and another point on said impedance, connectlons between saidpair of crystal electrodes and the control grids of said tubes, reactances of different character connected in shunt to the electrodes of said crystal, a pair of diode rectifiers eachhaving input and output electrodes, a band pass transformer coupling the input electrodes ofone of said diode rectifiers to the output electrodes of one of said tubes, a second band pass theothe'r of said diode rectifiers to the output electrodes of the other of said tubes, and a utilization circuit coupled to the output electrodes of said diode rectiflers.

7. v In a modulatedwave demodulatingand indicating system the combination of a plurality of filter circuits having similar but opposed output characteristics such that certain frequencies within the band passed thereby are exalted and others substantially rejected, rectifying means having inputs coupled to said filter circuits and having outputs coupled by impedances diilerentially responsive torectifled energynand meansfor amplifying the potentials, in the separate difierential impedances or the sum of the potentials in the diilerential impedances or the difference of the potentials in the differential impedances.

ton

' 8. In a system for adapting a phase or frequency modulated wave receiver of the type wherein a pair of filter circuits of opposed characteristics supply energy to detectors'having output electrodes differentially coupled by a pair of series impedances, one terminal of the series connection of which is connected to a point of substantially fixed potential, the combination of a pair of electron discharge devices each having an anode. a cathode, and a control grid, a connectlonbetween the cathodes of said devicesand said point of substantiallyv fixed potential, a connection between theanodes of said devices and an indicating circuit, an impedance connecting a relatively high potential end of each of said 7 I series resistances to said point of substantially fixed potential, a switch connected tothe control grid of each of said tubes and contacts cooperating with said switches for connecting different points on said impedances to said control grids.

9. In a phase or frequency or amplitude'modulated'waye energy eceiver, a wave energy amplifying and demodulating means of the heterodyne type including a detector cooperating with a local oscillator of controllable frequency to a cathode, and an anode, a connection between the cathodes of said tubes gdrcuit's are tuned to said circuits,

pro-

, l0 oscillator in accordance with the potentials across said imped- I ances, and voltage dividing means connected with said impedances for supplying therefrom the sum of the potentials produced thereacross and the difference, of .the potentials produced thereacross.

' -10. In a wave energy translating system, a tunable wave responsive means with means for impressing wave energy thereon, a frequency discriminating circuit including a piezoeelectric crystal having an input electrode coupled to said wave responsive means and a pair of output elec- /trodes, reactances shunted between said input electrode and each of said output electrodes to form therewith a pair of circuits one of which is eifectivelycapacitive and the other of which is effectively inductive with respect to the mean rectifiers coupled with said output electrodes for frequency of the 'wave energyimpressed from said means on said crystal input electrode,

producing a current componeri'tcharacteristic of v the reaction of the instantaneous mean frequency of said wave energy impressed on said crystal input electrode and the frequency at which said circuits are normally capacitive and inductive respectively, and means for tuning said tunable wave responsive means in accordance with said current component. 4 i 11. A system as recited in claim 7 wherein each of said filter circuits h ve a characteristic such that the carrier frequen y of said modulated wave is exalted.

12. A system as recited in claim 7 wherein each of said filter circuits have a characteristic such that one of said filters substantially rejectssideother side of said carrier frequency.

13. In a system for demodulating wave energy modulated in amplitude at signal frequency coinprising a carrier and sideband frequencies, a circuit having a characteristic which is reactive in the same sense with respect to a band of sideband sides of the frequency,

frequencies lying on both to which the circuit is tuned, a circuit having a characteristic which is reactive in the same sense, but opposite to the sense of the aforesaid circuit, with respect to a band of sideband frequencies lying on both sides of the frequency to which. the circuit is tuned, means for applying amplitude modulated wave energy of a mean frequency substantially equal to the frequency to-which said and detecting means coupled with said'circuits.

14. In a system for dem'odulating wave energy modulated in amplitude at signal frequency comprising a carrier and sideband frequencies, a

circuit having a characteristic which is reactive band frequencies lying on both sides of the frequency to which the circuit is tuned, means for applying amplitude-modulated wave energy the carrier wave frequency of which is substantially equal to the frequency to whichsaid circuits one only of which is connected to apoint oi.

substantially fixed potential, a pair of electron.

discharge devices having a control grid, 9; cathode and an anode, an output circuit connecting the anodes and cathodes of said devices in push-pull relation, 'a connection between the I cathodes of said devices and said point of substantially'fixed potential, two resistances connected between said point of substantially fixed potential and diflerent points on said imped ances, and switching means for connecting the control 'grid of each of said devices to diflerentv points on one only of said resistances.

16. In a system for demodulating phase'or irequency or amplitude modulated wave ener y;

pair of rectifiers having input and outp'utelectrodes, filter circuits of dissimilar characteristics coupled to the input electrodes of said rectifiers,"

a pair of impedances connecting the output electrodes of said rectifiers in a circuit, means for impressing modulated wave energy to be modulated on said filter circuits, whereby rectified current flows in said impedances to produce therein potentials characteristic of the said rectified current, and voltage dividing means 0on nected with said impedahces for supplying therefrom potentials which represent the diflerl'nce ent of the potentials produced by rectified cu in said impedances and potentials which repre-.- sent the summation of the potentials produced by rectified current in said impedances.

17. In a system for receiving amplitude modulated wave energy and demodulating the same, an impedance on which said wave energy is impressed, a pair of filter circuits each having an input coupled to said impedance and an output coupled to demodulating means, said filter circuits including a'c'rystal having three terminals one of which is common to said filters the other two of which are each in a different one of said filter circuits, reactive means in shunt to electrodes of said crystal in said. filter circuits for slightly o'fl' neutralizing said crystalwith re- 4 ,spect to-the wave energy whereby the carrier andcertain side jrequencies passed by each of said filter circuits are relatively exalted and,

other side frequencies are relatively reduced.

18. In a system for converting phase modulation on wave energy into corresponding amplitude modulations-an impedance, means for impressing phase modulated wave energy on said impedance, two pairs of .output terminals, an under-neutraiized crystal filter circuit, arr ibverneutralized crystal filter circuit, said filter circuits including a single piezo electric crystal havingone electrode connected to said impedance and having two other electrodes each. connected to an output terminal of a diflerentpair of said output terminals, a connection between a second point on said impedance and the re- 'maining terminal .0! each pair of output terminals, and a utilization circuit coupled to said pairs of output terminals.

19. In a system for converting wavelength modulations on wave energy into modulations ofa different type, an impedance, a plurality of output terminals, a piezo-electric crystal having a plurality of electrodes, means for impressing 'wave length modulated wave energy on said impedance; means coupling one. or said electrodes of said crystal to said impedance, means coupling other of said crystal electrodes each to one of said output terminals to form two filter circuits between said impedance and said output terminals, and means for relatively varying the degree of neutralization of the. reactance between pedan'ce, means coupling one oi,said electrodes of said crystal to said impedance, means coupling other of said crystal electrodesto a pair of said output terminals, means coupling a point on said impedance to another of said output terminals, and means for varying the degree of neutralization of the reactance between pairs of said crystal electrodes.

2 1. In -a system for converting wavelength 'modulations on wave energy intomodulations of a diiierent type, an impedance, a plurality of coupling tubes having input electrodes andhaving output electrodes coupled to a utilization means, means for impressing wave length modulated wave energy on .said impedance, a piezoelectric crystal having a plurality oi. electrodes,

electrodes, and ineans for varying the degree oi' neutralization o! the reactance between pairs of said crystal electrodes.

means coupling one of said crystal. electrodes to 22. In a systemior converting phase modulated wave energy to corresponding amplitude modulated wave energy, means for receiving said wave energy, a tunable oscillator coupled with said last named for beating local oscillations' with said received wave energywto produce coresponding wave energy of reducedfrequency,

, a reactance, means for impressing saidwave en-- ergyof reduced frequency .on said reactance, a piezc-electric crystal having an input electrode -and a pair of output electrodes, means coupling .said crystal input electrode to said reactance, a rectifier system having an input circuit and an output circuit including impedance, a circuit coupling one of the output electrodes of said crystal to. the input circuit of said-rectifier systern, a circuit coupling the other of said crystal output electrodes to the input circuit of said rectifier system, a coupling between said rectifier input circuit and said reactance, variable reactances connecting said reactance to each of said'crystal output electrodes, and means coupling said rectifier output circuit to said tunable lated-wave energy to corresponding amplitude modulated wave energy, means for receiving said oscillator to control the oscillator frequency in a s accordance with potentials at the output circuit of said rectifier. i .g 23. Int. system for..converting phase'modu- I A 9,904,674 reactance, meansfor. impressing said nave energy of reduced frequency on said-'reactance, a

plaza-electric crystal having an input electrode and a pair oi output electrodes, means coupling said crystal input electrode to said reactance, a

rectifier system having an input and an output circuit, means coupling the output circuit of said rectifier system to a utilization circuit, a circuit including coupling means tuned to substantially the mean frequency of said wave energy of reduced, frequency coupling one of the output electrodes of said crystal to the? input' circuit of said rectifier system a circuit includ- 7 inga coupling tuned to substantially the mean frequency of said wave energy of reduced frequency coupling the other of said crystal output electrodes to the input circuit of said rectifier system, .a coupling between the input circuit of said'rectifier system and said'first reactance, variable reactances coupling said first reactance to each of said crystal output electrodes, and a A circuit connecting the output of said rectifier system to said tunable oscillator to control the 10 tune thereof. I

' MURRAY G. CROSBY. 

